NASA images cloud streets over Norwegian Sea

WASHINGTON, March 25 (UPI) -- Cloud streets -- also known as horizontal convective rolls or horizontal roll vortices -- are long, straight bands of cumulus clouds. From above, they look like someone took a comb to a thin layer of clouds.

NASA's Aqua satellite recently spotted the phenomenon while passing above the Norwegian Sea. Aqua's Moderate Resolution Imaging Spectroradiometer camera, or MODIS, captured images of the clouds.

The unique bands form as cold winds blow across warmer waters and under an upper layer of warm air. As the lower air, warmed by the water, meets the cold air blowing above, moisture condenses. As this cloud-forming condensation continues to rise it bumps up against the layer of warm air above.

The temperature inversion acts as a lid, pushing the rising air back down. The air forms parallel cylinders. The ascending air features clouds, while the descending air is clear.

In the photo, cold air from the Arctic sea ice is moving southward across the Norwegian Sea toward Scandinavia.